Association between hypoxanthine concentration in synovial fluid and joint destruction in patients with rheumatoid arthritis

To evaluate the significance of augmented levels of hypoxanthine in synovial fluids in patients with rheumatoid arthritis (RA), the hypoxanthine level in the synovial fluid was investigated in association with joint damage. Concentrations of hypoxanthine, xanthine and uric acid in synovial fluids from knee joints of 45 patients with RA, six patients with gout and five patients with osteoarthritis were determined by high performance liquid chromatography. Relationships between these oxypurines and markers for joint inflammation or Larsen grade of knee joint X-ray film were analyzed. Hypoxanthine levels were significantly elevated in patients with RA and with gout but not in those with osteoarthritis. In RA patients, levels of synovial fluid hypoxanthine were correlated with matrix metalloproteinases MMP-3 (r=0.510), but not with C-reactive protein nor synovial fluid cytokines. Among various biological factors in synovial fluid (including cytokines and metalloproteinases) only hypoxanthine levels were significantly (P<0.05) positively correlated with Larsen’s grade of knee joint. In conclusion, augmented levels of synovial hypoxanthine can indicate joint damage in patients with RA and might be a useful marker in a clinical context.